Electric cars must be taxed to pay for more power stations or they could drain the National Grid and even contribute to power cuts, an energy firm has warned.

Analysts for Saturn Energy calculated that a fuel duty of up to 10p a mile would be required to pay for the extra demand which will be created if the Government’s targets on renewable energy are hit.

The Climate Change Committee has said that 1.7 million electric cars should be on Britain’s roads by 2020.

The firm’s experts said the National Grid was already struggling to provide enough power for Britain’s needs and urgent modernisation was required to boost capacity to provide for the needs of any surge in the number of electric cars.

The firm also said that electricity should cost “about the same as petrol”, which is certain to deter those motorists who are shifting to electric cars to try to save money on driving.